Compressor unloader



R. w. \VNILSON 2,715,992

COMPRESSOR UNLOADER Aug. 23, 1955 Filed June 26, 1951 INVENTOR noses u. wnson.

BYW4% H15 AT TORNEYE United States Patent COMPRESSOR UNLOADER Robert W. Wilson, Dayton, Ohio Application June 26, 1951, Serial No. 233,615

4 Claims. (Cl. 230-31) This invention relates to. a compressor unloader and more particularly to an unloader of the type in which a refrigerant bypass valve is provided for unloading one or more of the compressor cylinders when the suction pressure falls below a predetermined value.

It is now common practice in the refrigerant industry to provide one or more bypass valves directly in the cylinder head of a multiple cylinder compressor which serve to unload the compressor not only for starting purposes but also for unloading one or more of the cylinders when the capacity of the compressor exceeds the demand. A solenoid valve controlled by a switch which responds to the suction pressure is then used for operating the bypass valve. The difiiculty with a control of this type is that when the bypass valve moves from one position to the other, it momentarily permits some high side refrigerant to escape to the low side of the compressor so as to momentarily build up the low side pressure to a point where it causes the pressure responsive unloader to re-close the bypass valve. This then results in a hunting action which is very objectionable. It is an object of this invention to provide an arrangement whereby the momentary inrush of high pressure gas into the suction line will not cause the unloader to reload the compressor.

Other objects and advantages reside in the construction of parts, the combination thereof and the mode of operation, as will become more apparent from the following description.

In the drawing: 7

Figure 1 is a fragmentary sectional elevational view diagrammatically showing my control applied to a compressor; and

Figure 2 is a sectional view somewhat diagrammatic showing the construction of the check valve which is provided in the refrigerant line leading to the pressure operated unloader control switch.

For purposes of illustrating my invention, it has been shown applied to a refrigerating system, whereas it could also be applied to air compressor systems and the like.

Referring now to the drawing wherein there is shown a preferred embodiment of my invention, reference numeral 10 is intended to designate one cylinder of a conventional multiple cylinder compressor provided with an unloader control embodying my invention. Reference numerals 12 and 14 designate the condenser and evaporator respectively of a refrigeration system. The compressed refrigerant normally leaves the compressor through the high pressure refrigerant line 16 which conveys the compressed refrigerant gas to the condenser 12 wherein the refrigerant is condensed. The condensed refrigerant then flows through a suitable pressure reducing device 18 into the evaporator 14 where the refrigerant vaporizes before returning to the suction side of the compressor through the low pressure suction line 20.

In air conditioning installations, for example, it is Ea'iertted Aug. 23, 1955 desirable to modulate the output of the compressor, so as to prevent the suction pressure from going below the point where the evaporator would operate at temperatures low enough to freeze the condensate. This may be done by unloading one or more of the cylinders of the compressor.

In the system shown in the drawing, an unloader valve 34) has been provided for selectively connecting the outlet 32 of the compressor either to the high pressure refrigerant line 16 or to the bypass 34 which connects to the low pressure suction line 20, as shown. When the valve 30 is in the position in which it is shown in Figure 1 of the drawing, all of the compressed refrigerant is required to flow into the relatively high pressure line 16 wherein the pressure may, for example, be in the neighborhood of 120 lbs. per square inch. When the valve 30 moves from the solid line position into its dotted line position, the compressed refrigerant leaving the outlet 32 is directed to the compressor inlet or low pressure side of the system through the bypass 34, with the result that the effectiveness of the cylinder to which the bypass is attached is destroyed.

The unloader valve 30 is connected to the piston 40, the operation of which is controlled by the two-way valve 36, which in turn is controlled by the solenoid 38. When the two-way valve 36 is in the position in which it is shown, the upper end of the piston 40 is subjected to the low side pressure and will move to the closed position under the influence of the spring 42, since the pressure of the refrigerant will be the same on both sides of the piston 40. When the valve'36 is lifted by the solenoid 38, the upper end of the piston 40 will be connected to the high side pressure and will be forced downwardly so as to open the bypass and close off the flow of compressed refrigerant into the line 16.

The solenoid 38 is controlled by the switch 44, which in turn is controlled by the pressure operated bellows 46 arranged as shown. The bellows 46 is normally subjected to a pressure corresponding to the pressure in the suction line through the capillary tube 48, the accumulator chamber 50, and the check valve 52. Except for the check valve 52 and the accumulator 5d, the system as thus far described represent the unloaders as now used in the industry.

It has been found that as the unloader valve 30 moves to the unloading position, gas in the line 16, which at times may be at a pressure considerably in excess of lbs. per square inch, tends to rush past the unloader valve through the bypass 34 and to the suction line 20, thereby giving a false indication that the suction line pressure is considerably in excess of that at which the compressor should be unloaded. In the prior unloader control systems which do not have the check valve 52 and the accumulator 50, this would cause the switch 44 to operate the unloader valve to momentarily re-close and thereby produce a hunting action. By adding the check valve 52 and the accumulator 50, any momentary increase in the suction line pressure will be inefiective to re-close the unloader valve. It will be noted that the check valve 52 includes a conventional check valve disc or plate 54 in which there is provided a small leak port or restricted passage 56 which permits a prolonged difference in pressure to become equalized. However, any sudden decrease in the suction pressure will immediately be transmitted to the bellows 46, as the check valve disc or plate 54 is free to open in the event of any such sudden decrease.

The check valve 56 also makes it possible for any oil trapped above the check valve plate 54 to freely flow down past the valve in response to reduction in the suction pressure. The accumulator chamber 50, in

' fined in the appended claims.

conjunction with the restricted passage 56, serves to prevent re-closing of the unloader valve in response to-the momentary inrush of, high pressure gas from the 7 line 16 to the suction side of the compressor butdoes not. prevent the switch'from responding to prolonged high suction pressures or to momentary reductions in the 'suction pressure below the pressure at; which the switch is set to ,Operate.

' In a conventional air conditioning installatiom the switch would be set toclose the circuit to the solenoid 38 when the suction pressure'drops below 28 lbs. per square inch, so as to unload the compressor and therei by prevent-the frosting ofthe evaporator I Theiunloader :control shown herein could also be used with single cylinder compressorswherein it is desired to operate the compressor'continuously and to control the operation'of the system by unloading the compressor rather than by starting and stopping the compressor. I V

The control system shown herein would normally be built into refrigerationisystems when first manufactured, but for those systems now in the field one would merely add the check valve and accumulator into the capillary'line leading to the switch operating bellows 46.

Although the preferred embodimentof the device has been described, it will be understood that within the purview of this'inventio'n various changes may be made 7 in theform, details, proportion and arrangement of parts, the combination thereof and mode of operation,

7 which generally stated consist in a device capable of carrying outthe objects set forth, as disclosed and de- 7 Having thus described my invention, I clairnz 1. In combination' with a compressor having a: low

7 1 pressure suction inlet and a relatively high pressure out-i let, means forming a compressor unloading bypass between said inlet and said outlet, a valve for controlling the flow throughsaid bypass and for shutting oil? the flow through saidioutlet, means for controlling the op- V eration of said valve including a pressure responsive device, means'for connecting said pressure responsive device to said suction inlet, a check valve in said last named'means for checking the flow from said inlet to said pressure responsive device, and means forming a' restricted passage at all times providing a passage between said compressor inlet and said pressure responsive device even when said check valve is closed.

2. In combination with a compressor having a low pressure suction inlet and a relatively high pressure-outlet, means forming a bypass between said inlet, and

passage at all times connecting said suction line and said device.

3. In a control device adapted to be connected to' the suction side of a compressor for regulating the unloading of the compressor in response to changes in the.

suction pressure, the combination,*a pressure responsive control, conduit means connecting said pressure V responsive control to the suction side of the compressor, a surge chamber intermediate the end of said -conduit: means, a check valve disposed between said surge chamber and the suction side of saidfco mpressor for j checking the flow'into said surge chamber, and means forming a leak port for bypassing said ,check'valve.

4.' In a control device adapted to be connected to' thesuctionside of a compressor for regulating the unloading of they compressor; in response to changes in' the suction pressure, ithecombination, a pressure re-I sponsive control, conduit means connecting said pressureresponsivetontrol tofth'e suction side of the compressor, a surgev chamber intermediate the ends of said conduit means, acheck valve disposed between said surge chamber and the suction side of said compres sor for checking the flow into said surge chamber, and means forming a leak port for bypassing said check valve, said last namedmeans: comprising an aperture provided'in said check valve whereby said control de-' vice isunafiect ed by momentary increases in suction pressure. 7 I 7 References Cited in the file ofthis patent V UNITED STATES; PATENTS 1,105,061 Carpenter'- July 28, 1914 1,742,407 "McCu'ne Jan. 7, 1930 1,920,003 j Chenault'; Ju1y;25,*1933 1,956,962 Ringle Mayyl', 1934 2,006,584 De Puy "July 2, 1935 2,123,123 Small et a1. July '5, "1938 2,531,315 Wyllie- .a; Nov. 21, 1950 2,577,902 McGrath Dec. 11, 

